A thermodynamic approach for assessing the environmental exposure of chemicals absorbed to microplastic

The environmental distribution and fate of microplastic in the marine environment represents a potential cause of concern. One aspect is the influence that microplastic may have on enhancing the transport and bioavailability of persistent, bioaccumulative, and toxic substances (PBT). In this study we assess these potential risks using a thermodynamic approach, aiming to prioritize the physicochemical properties of chemicals that are most likely absorbed by microplastic and therefore ingested by biota. Using a multimedia modeling approach, we define a chemical space aimed at improving our understanding of how chemicals partition in the marine environment with varying volume ratios of air/water/organic carbon/polyethylene, where polyethylene represents a main group of microplastic. Results suggest that chemicals with log KOW > 5 have the potential to partition >1% to polyethylene. Food-web model results suggest that reductions in body burden concentrations for nonpolar organic chemicals are likely to occur for chemicals with log KOW between 5.5 and 6.5. Thus the relative importance of microplastic as a vector of PBT substances to biological organisms is likely of limited importance, relative to other exposure pathways. Nevertheless, a number of data-gaps are identified, largely associated with improving our understanding of the physical fate of microplastic in the environment.